Encryption Decryption Question:

What are the CFB and OFB modes?

Answer:

The Cipher Feedback (CFB) mode and the Output Feedback (OFB) mode are two more standard modes of operation for a block cipher.

In CFB mode, the previous ciphertext block is encrypted and the output produced is combined with the plaintext block using exclusive-or to produce the current ciphertext block. It is possible to define CFB mode so that it uses feedback that is less than one full data block. An initialization vector or value c0 is used as a "seed" for the process.